As microelectronic circuit designs become ever larger, larger integrated circuit packages are also necessary as a result of the extra signal and supply interconnections of the larger microelectronic circuits. Referring to FIG. 1, a printed circuit board assembly, according to the conventional art, is shown. The PCBA 100 typically includes a printed circuit board 110 and a plurality of integrated circuit (IC) packages and one or more discrete electronic components. Conventional IC packages include an integrated circuit (IC) die 120 and a package substrate 130. The IC package may also include an encapsulant 140, thermal dissipation element or combination thereof to provide thermal dissipation, electrical, mechanical, and/or environmental protection. The package substrate 130 is adapted to electrically couple the IC die 120 to a printed circuit board (PCB) 110. In particular, the IC die 120 includes a plurality of connection pads disposed on a first surface. The package substrate 130 includes a plurality of connection pads disposed on a first surface that correspond to the plurality of connection pads on the IC die 120. The connection pads on the first surface of the package substrate 130 are adapted to be electrically coupled to respective connection pads on the IC die 120, typically by reflowing solder bumps 150 on the connection pads of the package substrate 130 and/or IC die 120. The plurality of connection pads on the first side of the package substrate 130 are electrically coupled to a plurality of connection pads on a second side of the package substrate 130 by a plurality of vias. The connection pads on the second side of the package substrate 130 are adapted to be electrically coupled to connection pads on the PCB 110, typically by reflowing solder balls 160 of the package substrate 130 and/or the PCB 110. Alternatively, the substrate 130 may employ connection pins on the second side of the package substrate 130 that mate with plated-through-holes or a socket on the PCB 110.
Conventional pin grid array (PGA) packages typically have a maximum I/O connection density of approximately 600 connections, and ball grid array (BGA) packages have a maximum density of approximately 1000. Chip scale packages, flip-chip packages, and the like typically employ bump grid arrays and can achieve greater connection densities. Typically the connection density is limited by the minimum area of the bond pads and minimum distance between adjacent bond pads. For reliable connection with a PCB, it becomes increasingly more expensive to further miniaturize the area of the bond pads and spacing between the pads. Accordingly, at some point conventional package substrates become unwieldy large due to the large number of connection regions that must be fabricated on the surface that is coupled to the PCB.